In automatic transmissions of automobiles, fluid pressure is used to engage clutches and shift the transmission between its various gears. The fluid in such automatic transmissions is often at high temperatures and pressures. As a result, the seals used in automatic transmissions are frequently required to withstand severe operating conditions.
Some automotive transmission designs transmit fluid pressure through cylindrical gaps or cavities surrounding a rotating shaft. In such designs, the seals are positioned in grooves that extend circumferentially about the shaft. The seals are generally ring shaped and rectangular in cross section. The seals span the gaps between the shaft and a surrounding cylindrical wall which bounds the gaps.
In some transmissions which have seals of this type, fluid pressure applies a sideways or axial force to the seal. These forces can cause the seal to deform and extrude into the gap between the outer wall of the shaft and the cylindrical wall bounding the gap. The axial forces can also cause the sides of the seals to wear rapidly as the seal is pushed against the walls of the groove.
In such automatic transmission applications, the seals are subjected to alternative pressure forces in both directions. This occurs as the transmission changes gears. These periodic forces in alternating directions can rapidly wear a seal and cause failure.
Thus, there exists the need for a seal that can prevent fluid flow through a gap between a shaft and a cylindrical wall bounding the gap in an automatic transmission. There is a further need for a seal that can withstand high fluid temperatures and pressures, and which has a longer service live.